The present invention relates generally to wavelength division multiplexing and demultiplexing and, more particularly, to bi-directional wavelength division multiplexing/demultiplexing devices.
Wavelength division multiplexing (WDM) is a rapidly emerging technology that enables a very significant increase in the aggregate volume of data that can be transmitted over optical fibers. Prior to the use of WDM, most optical fibers were used to unidirectionally carry only a single data channel at one wavelength. The basic concept of WDM is to launch and retrieve multiple data channels into and out of, respectively, an optical fiber. Each data channel is transmitted at a unique wavelength, and the wavelengths are appropriately selected such that the channels do not interfere with each other, and the optical transmission losses of the fiber are low. Today, commercial WDM systems exist that allow for the transmission of 2 to 100 simultaneous data channels.
WDM is a cost-effective method of increasing the volume of data (commonly termed bandwidth) transferred over optical fibers. Alternate competing technologies for increasing bandwidth include the burying of additional fiber optic cable or increasing the optical transmission rate over optical fiber. The burying of additional fiber optic cable is quite costly as it is presently on the order of $15,000 to $40,000 per kilometer. Increasing the optical transmission rate is limited by the speed and economy of the electronics surrounding the fiber optic system. One of the primary strategies for electronically increasing bandwidth has been to use time division multiplexing (TDM), which groups or multiplexes multiple lower rate electronic data channels together into a single very high rate channel. This technology has for the past 20 years been very effective for increasing bandwidth. However, it is now increasingly difficult to improve transmission speeds, both from a technological and an economical standpoint. WDM offers the potential of both an economical and technological solution to increasing bandwidth by using many parallel channels. Further, WDM is complimentary to TDM. That is, WDM can allow many simultaneous high transmission rate TDM channels to be passed over a single optical fiber.
The use of WDM to increase bandwidth requires two basic devices that are conceptually symmetrical. The first device is a wavelength division multiplexer. This device takes multiple beams, each with discrete wavelengths that are initially spatially separated in space, and provides a means for spatially combining all of the different wavelength beams into a single polychromatic beam suitable for launching into an optical fiber. The multiplexer may be a completely passive optical device or may include electronics that control or monitor the performance of the multiplexer. The input to the multiplexer is typically accomplished with optical fibers, although laser diodes or other optical sources may also be employed. As mentioned above, the output from the multiplexer is a single polychromatic beam which is typically directed into an optical fiber.
The second device for WDM is a wavelength division demultiplexer. This device is functionally the opposite of the wavelength division multiplexer. That is, the wavelength division demultiplexer receives a polychromatic beam from an optical fiber and provides a means of spatially separating the different wavelengths of the polychromatic beam. The output from the demultiplexer is a plurality of monochromatic beams which are typically directed into a corresponding plurality of optical fibers or photodetectors.
Currently, the commercial use of WDM systems is mainly for long haul, point-to-point telecommunication applications. Such WDM systems are typically only uni-directional traffic systems as the cost and complexity of implementing bi-directional WDM traffic systems is presently quite high. For example, two sets of unique WDM devices are typically required to implement bi-directional WDM traffic systems. That is, one WDM device in each set is typically used for multiplexing a plurality of monochromatic beams from a laser diode array or other optical sources to a single output fiber. Another WDM device in each set is typically used in the opposite direction for demultiplexing a polychromatic beam from a single input fiber to a photodetector array or a plurality of output fibers.
Due the above-described cost and complexity associated with implementing bi-directional WDM traffic systems, it is easily understandable that it would be very desirable to provide bi-directional WDM devices to increase the utility of WDM systems. This increase in utility is particularly important for using WDM technology in local area network (LAN) systems, which are increasingly in need of additional bandwidth and typically operate in environments having shorter distances than long haul, point-to-point telecommunication applications. Also, the use of WDM technology allows a significant increase in the amount of information that can be transferred over an optical fiber. However, system size and cost are critical factors in LAN systems. Thus, as of today, the use of WDM technology for LAN-type networks has not occurred due to the high cost and complexity of WDM systems. However, it is predicted that the ever-increasing need for bandwidth will make the use of WDM-based LAN systems very attractive within the next ten years.
In view of the foregoing, it would be desirable to provide bi-directional WDM devices which overcome the above-described inadequacies and shortcomings. More particularly, it would be desirable to provide bi-directional WDM devices for use in implementing bi-directional WDM traffic systems in an efficient and cost effective manner.
The primary object of the present invention is to provide bi-directional WDM devices for use in implementing bi-directional WDM traffic systems in an efficient and cost effective manner.
The above-stated primary object, as well as other objects, features, and advantages, of the present invention will become readily apparent to those of ordinary skill in the art from the following summary and detailed descriptions, as well as the appended drawings. While the present invention is described below with reference to preferred embodiment (s), it should be understood that the present invention is not limited thereto. Those of ordinary skill in the art having access to the teachings herein will recognize additional implementations, modifications, and embodiments, as well as other fields of use, which are within the scope of the present invention as disclosed and claimed herein, and with respect to which the present invention could be of significant utility.
According to the present invention, a bi-directional wavelength division multiplexing/demultiplexing device is provided. In a first exemplary embodiment, the bi-directional wavelength division multiplexing/demultiplexing device comprises a diffraction grating for combining a plurality of monochromatic optical input beams into a multiplexed, polychromatic optical output beam, and for separating a multiplexed, polychromatic optical input beam into a plurality of monochromatic optical output beams; and a transmissive/reflective optical element for transmitting the plurality of monochromatic optical input beams on an optical path toward the diffraction grating, and for reflecting the plurality of monochromatic optical output beams received on an optical path from the diffraction grating.
In accordance with other aspects of the present invention, the diffraction grating may be a transmissive diffraction grating. If such is the case, the bi-directional wavelength division multiplexing/demultiplexing device further beneficially comprises a first collimating/focusing lens for collimating the plurality of monochromatic optical input beams, and for focusing the multiplexed, polychromatic optical output beam; and a second collimating/focusing lens for collimating the multiplexed, polychromatic optical input beam, and for focusing the plurality of monochromatic optical output beams. Then, the transmissive/reflective optical element is preferably located opposite either the first collimating/focusing lens or the second collimating/focusing lens from the diffraction grating. Alternatively, the transmissive/reflective optical element may be located between the diffraction grating and either the first collimating/focusing lens or the second collimating/focusing lens.
In accordance with other aspects of the present invention, the diffraction grating may instead be a reflective diffraction grating. If such is the case, the bi-directional wavelength division multiplexing/demultiplexing device further beneficially comprises a collimating/focusing lens for collimating the plurality of monochromatic optical input beams and the multiplexed, polychromatic optical input beam, and for focusing the multiplexed, polychromatic optical output beam and the plurality of monochromatic optical output beams, respectively. Then, the transmissive/reflective optical element is preferably located opposite the collimating/focusing lens from the diffraction grating. Alternatively, the transmissive/reflective optical element may be located between the diffraction grating and the collimating/focusing lens.
In accordance with further aspects of the present invention, the transmissive/reflective optical element is either a passive optical element or an active optical element. For example, the transmissive/reflective optical element may be a passive beamsplitter having a 45 degree reflecting angle and a fixed transmission/reflection ratio. Alternatively, for example, the transmissive/reflective optical element could be an active electrooptical element also having a 45 degree reflecting angle, but with a variable transmission/reflection ratio.
In a second exemplary embodiment, the bi-directional wavelength division multiplexing/demultiplexing device comprises a diffraction grating for combining a plurality of monochromatic optical input beams into a multiplexed, polychromatic optical output beam, and for separating a multiplexed, polychromatic-optical input beam into a plurality of monochromatic optical output beams; and a transmissive/reflective optical element for reflecting the plurality of monochromatic optical input beams on an optical path toward the diffraction grating, and for transmitting the plurality of monochromatic optical output beams received on an optical path from the diffraction grating.
The present invention will now be described in more detail with reference to exemplary embodiments thereof as shown in the appended drawings.